Tunable balanced loss compensation in an electronic filter

ABSTRACT

The invention provides a system for providing tunable balanced loss compensation in an electronic filter. Tunable balanced loss compensation is provided by using cross-connected balanced transconductors and self-connected balanced transconductors. The cross-connected balanced transconductors and the self-connected transconductors compensate the unbalanced loss across the electronic filter. The self-connected balanced transconductors compensate the balanced loss across the electronic filter. Further, the cross-connected and the self-connected balanced transconductors are tunable by adjusting the values of their transconductances, thereby providing tunable balanced loss compensation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of electronic filters. More specifically, the present invention relates to a system providing tunable, balanced loss compensation for an unbalanced electronic filter.

2. Description of the Related Art

In communication systems, electronic filters are used for signal processing. Electronic filters eliminate unwanted frequencies from an electronic signal. Different types of electronic filters, such as low-pass filters, band-pass filters, high-pass filters, active filters and passive filters, may be used for this purpose. An electronic filter is usually a combination of inductors and capacitors, referred to as an LC circuit. The electronic filter may include one or more LC circuits and may consist of balanced and unbalanced structures. Examples of balanced structures include balanced LC oscillators and shunt LC resonators. Examples of unbalanced structures include series LC resonators.

The inductors and capacitors in electronic filters have a resistive component that causes losses in the electronic filter during transmission. These losses result in a decrease in the quality of the frequency response provided by the electronic filter. Hence, losses in the electronic filter need to be compensated. Moreover, these losses in the electronic filter may vary with the process, temperature and other factors. Therefore, loss compensation in the electronic filter needs to be tunable, so that it may be adjusted according to the variations in the losses.

Existing methods and systems provide loss compensation for a balanced structure in an electronic filter by using a cross-coupled pair of transistors. This cross-coupled pair of transistors, referred to as a negative resistor, compensates for the resistive losses in a balanced structure. However, the cross-coupled pair of transistors, when used for loss compensation in an unbalanced structure, results in the development of even-order harmonics. These even-order harmonics are undesirable since they distort the frequency response of the electronic filter.

In light of the foregoing discussion, there exists a need for a system to provide tunable loss compensation in an electronic filter. Further, the system provides balanced loss compensation for an unbalanced structure in the electronic filter.

SUMMARY OF THE INVENTION

An object of various embodiments of the invention is to provide a balanced loss compensation for unbalanced and balanced losses in electronic filters.

Another object of various embodiments of the invention is to provide tunable balanced loss compensation in the electronic filters.

To achieve the foregoing objects, in accordance with the purpose of the invention, as broadly described herein, the invention provides a system for providing tunable balanced loss compensation in an electronic filter. The system includes a first set and a second set of transconductors. The first set of transconductors includes at least two cross-connected balanced transconductors, and the second set of transconductors includes at least two self-connected balanced transconductors. The at least two cross-connected balanced transconductors are connected across the balanced input and output ports of the electronic filter. One of the at least two self-connected balanced transconductors is connected between the two terminals of the balanced input port of the electronic filter. Another of the at least two self-connected balanced transconductors is connected between the two terminals of the balanced output port of the electronic filter. The at least two self-connected balanced transconductors compensate the balanced loss across the electronic filter. The at least two self-connected balanced transconductors and the at least two cross-connected balanced transconductors compensate the unbalanced loss across the electronic filter. The loss compensation is tunable by adjusting the transconductances of the at least two cross-connected balanced transconductors and the at least two self-connected balanced transconductors at the design stage of the electronic filter.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to various embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 is a schematic circuit diagram illustrating a system for providing loss compensation, in accordance with an embodiment of the invention;

FIG. 2 is a schematic circuit diagram used to illustrate the operation of balanced loss compensation in an unbalanced structure; and

FIG. 3 is a circuit diagram illustrating loss compensation in an IF filter of a double conversion TV tuner, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

Various embodiments of the invention provide a system for loss compensation in an electronic filter. The loss in an electronic filter may be a balanced loss or an unbalanced loss. The type of loss depends on the type of the electronic filter, such as a series LC resonator, a shunt LC resonator, or a combination thereof. The system includes a first set and a second set of transconductors. The first set of transconductors includes at least two cross-connected balanced transconductors, and the second set of transconductors includes at least two self-connected balanced transconductors. The at least two self-connected balanced transconductors compensate the balanced loss across the electronic filter. The at least two self-connected balanced transconductors and the at least two cross-connected balanced transconductors compensate the unbalanced loss across the electronic filter. Further, the at least two cross-connected balanced transconductors and the at least two self-connected balanced transconductors are tunable, thereby providing tunable balanced loss compensation.

FIG. 1 is a schematic circuit diagram illustrating a system 100 for providing tunable and balanced loss compensation, in accordance with an embodiment of the invention. System 100 includes at least four transconductors 102 a, 102 b, 102 c, and 102 d, and two resistors 104 a and 104 b. System 100 also includes a differential balanced input port 106 and a differential balanced output port 108. Balanced input port 106 has positive terminal 106 a and negative terminal 106 b. Balanced output port 108 has positive terminal 108 a and negative terminal 108 b.

In various embodiments of the invention, system 100 provides tunable and balanced loss compensation in an electronic filter (not shown in FIG. 1). The electronic filter has an unbalanced structure. Signals are provided to the electronic filter through balanced input port 106. Resistors 104 a and 104 b, as shown in FIG. 1, represent the resistive losses in the electronic filter. Resistor 104 a is connected between positive terminal 106 a of balanced input port 106 and positive terminal 108 a of balanced output port 108 of the electronic filter. Similarly, resistor 104 b is connected between negative terminal 106 b of balanced input port 106 and negative terminal 108 b of balanced output port 108 of the electronic filter.

In one embodiment of the invention, the loss across resistors 104 a and 104 b is unbalanced since the signals at the two ends of the resistors 104 a and 104 b are different. In other words, the signals at the two ends of the electronic filter are unsymmetrical.

Transconductors 102 a and 102 b are Self-Connected Balanced Transconductors (SCBTs). Transconductors 102 a and 102 b will herein after be referred to as SCBTs 102 a and 102 b. SCBT 102 a is connected across balanced input port 106 of the electronic filter. The positive input of SCBT 102 a is connected to positive terminal 106 a of balanced input port 106. Similarly, the negative input of SCBT 102 a is connected to negative terminal 106 b of balanced input port 106. SCBT 102 b is connected across balanced output port 108 of the electronic filter, in a similar manner as SCBT 102 a.

Transconductors 102 c and 102 d are Cross-Connected Balanced Transconductors (CCBTs). Transconductors 102 c and 102 d will herein after be referred to as CCBTs 102 c and 102 d. CCBTs 102 c and 102 d are connected across the input and output ports of the electronic filter. The negative output of CCBT 102 c is connected to positive terminal 106 a of balanced input port 106. The positive output of CCBT 102 c is connected to negative terminal 106 b of balanced input port 106. In a similar manner, the negative output of CCBT 102 d is connected to positive terminal 108 a of balanced output port 108. The positive output of CCBT 102 d is connected to negative terminal 108 b of balanced output port 108.

The four transconductors 102 a, 102 b, 102 c, and 102 d provide a tunable balanced loss compensation for the unbalanced loss in the electronic filter. SCBTs 102 a and 102 b compensate the balanced loss across the electronic filter. SCBTs 102 a and 102 b and CCBTs 102 c and 102 d compensate the unbalanced loss across the electronic filter. The concept of providing a balanced loss compensation across an unbalanced structure is explained in conjunction with FIG. 2

In various embodiments of the invention, SCBTs 102 a and 102 b and CCBTs 102 c and 102 d include a pair of cross-coupled transistors (not shown). In other words, the base of one transistor is connected to the collector of the other. Further, the emitters of the two transistors are connected to the ground or a virtual ground. In one embodiment of the invention, the base connections of the two transistors are taken as the positive terminals of a transconductor. The emitters of both the transistors are taken as the negative terminals of the transconductor.

In an embodiment of the invention, the transconductance (G_(m)) of SCBTs 102 a and 102 b, and CCBTs 102 c and 102 d compensates the loss in the electronic filter. G_(m) is the ratio of the change in the output current to the change in the input voltage of transconductor 102. Therefore, G_(m) is the reciprocal of resistance. In one embodiment of the invention, the G_(m) of SCBTs 102 a and 102 b, and CCBTs 102 c and 102 d may be equal to the reciprocal of resistors 104 a and 104 b, for ideal loss compensation.

In an embodiment of the invention, the G_(m) of SCBTs 102 a and 102 b, and CCBTs 102 c and 102 d may be adjusted at the design stage of the electronic filter, to provide tunable loss compensation. The G_(m) of SCBTs 102 a and 102 b, and CCBTs 102 c and 102 d are adjusted at the design stage in order to achieve the desired selectivity of frequency response of the electronic filter. In various embodiments of the invention, the G_(m) of transconductor 102 may be adjusted by altering the biasing condition of the transistors. The biasing condition of the transistors may be altered by adjusting the voltage applied across the positive terminals of the pair of cross-coupled transistors.

In an embodiment of the invention, the SCBTs 102 a and 102 b, and CCBTs 102 c and 102 d may have the same transconductance. In another embodiment of the invention, SCBTs 102 a and 102 b, and CCBTs 102 c and 102 d may have different transconductance.

In accordance with various embodiments of the invention, the electronic filter may include one or more LC resonators. The LC resonators in the electronic filter may include inductors and varactor diodes, which act as variable capacitors, such as discussed in connection with the circuit illustrated in FIG. 3 for an intermediate frequency filter. An LC resonator has a certain resonant frequency at which the electric current alternates between the inductor and the capacitor. Thus, the LC resonator filters signals around this resonant frequency and functions like an electronic filter.

In various embodiments of the invention, the Q factor of the electronic filter, i.e., the selectivity of the electronic filter's rejection of unwanted signals may be adjusted by changing the transconductances of SCBTs 102 a and 102 b, and CCBTs 102 c and 102 d.

In accordance with various embodiments of the invention, the electronic filter may be, for example, a low-pass filter, a high-pass filter, a band-pass filter, a LC filter, and the like.

FIG. 2 is a schematic circuit diagram used to illustrate the operation of balanced loss compensation in an unbalanced structure. The circuit includes an input port 202, an output port 204, two resistors 206 a and 206 b, two negative resistances 206 c and 206 d, and four voltage-controlled-current sources 208 a, 208 b, 208 c and 208 d.

Input port 202 may be the input port of an electronic filter such as input port 106. Similarly, output port 204 may be the output port of an electronic filter such as output port 108. Resistors 206 a and 206 b may represent the resistive losses in the LC resonators in the electronic filter.

Resistors 206 a and 206 b are connected in series between input port 202 and output port 204. Hence, the loss across resistors 206 a and 206 b is unbalanced. The resistive loss between two nodes in a circuit may be modeled as a combination of the loss across a resistor and a voltage-controlled current source, connected between each node and the ground. As shown in FIG. 2, the loss across resistor 206 may be split into the losses between input port 202 and the ground, and output port 204 and the ground. The loss between input port 202 and the ground is equivalent to the resistive loss across resistor 206 a and voltage-controlled-current source 208 a between input port 202 and the ground. Similarly, the loss between output port 204 and the ground is equivalent to the resistive loss across resistor 206 b and voltage-controlled-current source 208 b between output port 204 and the ground.

The loss between input port 202 and the ground is compensated by connecting a negative resistor 206 c and an inverted voltage-controlled-current source 208 c to the ground. Similarly, the loss between output port 204 and the ground is compensated by connecting negative resistor 206 d and inverted voltage-controlled-current source 208 d to the ground. This provides balanced loss compensation for the unbalanced loss in the circuit. A negative resistor is a system, which outputs more energy than the input energy. This is in contrast to a positive resistor, which dissipates the energy passing through it. By way of example, a cross-coupled transistor pair may be a negative resistor.

The loss compensation provided by negative resistors 206 and inverted voltage-controlled-current sources 208 is similar to the loss compensation provided by transconductors 102, in various embodiments of the invention.

The system for providing loss compensation in an electronic filter may be used to compensate the unbalanced loss occurring in an intermediate frequency (IF) filter such as in a double conversion TV tuner.

An Intermediate Frequency (IF) filter is an electronic filter that filters intermediate frequency signals. The range of intermediate frequency signals depends on the specific application. A double-conversion TV tuner tunes television signals. The TV tuner translates radio frequency signals into intermediate frequency (IF) signals and subsequently into the desired lower-frequency signals. The IF filter includes a plurality of LC circuits. Hence, a balanced loss compensation is required. Loss compensation in an IF filter is explained in detail in conjunction with FIG. 3.

FIG. 3 is a circuit diagram illustrating loss compensation in an IF filter of a double conversion TV tuner, in accordance with an embodiment of the invention. The figure illustrates the application of the circuit illustrated in FIG. 1 in an IF filter of a double conversion TV tuner. The IF filter includes four LC resonators 302 a, 302 b, 302 c, and 302 d, a balanced input port 306, and a balanced output port 308. In accordance with various embodiments of the invention, four transconductors 304 a, 304 b, 304 c, and 304 d provide balanced and tunable loss compensation in the IF filter.

In various embodiments of the invention, transconductors 304 a and 304 b may be SCBTs 102 a and 102 b. Transconductors 304 a and 304 b will herein after be referred to as SCBTs 304 a and 304 b. Similarly, transconductors 304 c and 304 d may be CCBTs 102 c and 102 d.

Transconductors 304 c and 304 d will herein after be referred to as CCBTs 304 c and 304 d. In an embodiment of the invention, the values of G_(m) of SCBTs 304 a and 304 b are different from the values of G_(m) of CCBTs 304 c and 304 d.

LC resonators 302 a and 302 b are connected in a shunt manner across balanced input and output ports 306 and 308, respectively. LC resonator 302 a is connected across the two terminals 306 a and 306 b of balanced input port 306. LC resonator 302 b is connected across two terminals 308 a and 308 b of balanced output port 308. LC resonator 302 c is connected in series between positive terminal 306 a of input port 306 and positive terminal 308 a of output port 308. LC resonator 302 d is connected in series between negative terminal 306 b of input port 306 and negative terminal 308 b of output port 308.

The loss across LC resonators 302 a and 302 b is balanced as signals at the two ends of LC resonators 302 a and 302 b have the same amplitude, but are out of phase with each other. The loss across LC resonators 302 c and 302 d is unbalanced as the signals at the two ends of LC resonators 302 c and 302 d are unsymmetrical. The compensation of the balanced and unbalanced losses across LC resonators 302 a, 302 b, 302 c, and 302 d is explained in conjunction with the following paragraphs.

The losses across LC resonators 302 a, 302 b, 302 c and 302 d are compensated by SCBTs 304 a and 304 b and CCBTs 304 c and 304 d. The balanced loss across LC resonator 302 a is compensated by SCBT 304 a. The balanced loss across LC resonator 302 b is compensated by SCBT 304 b. The unbalanced loss across LC resonator 302 c is compensated by SCBT 304 a, SCBT 304 b, CCBT 304 d and CCBT 304 c. Similarly, the unbalanced loss across LC resonator 302 d is compensated by SCBT 304 a, SCBT 304 b, CCBT304 c and CCBT 304 d. The loss compensation achieved by SCBTs 304 a and 304 b and CCBTs 304 c and 304 d is balanced.

Various embodiments of the invention provide an efficient system for loss compensation in an electronic filter. The loss compensation provided by the system is balanced. The system provides loss compensation in an unbalanced structure in an electronic filter. Further, the system provides tunable loss compensation to achieve the desired quality of the filter response. In an embodiment of the invention, the system may be implemented on a single integrated circuit.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

1. A system for providing loss compensation in an electronic filter, the system comprising: a first set of transconductors, the first set of transconductors comprising at least two balanced transconductors, the at least two balanced tranconductors being cross-connected with each other, the at least two cross-connected balanced tranconductors being connected across balanced input and output ports of the electronic filter; and a second set of transconductors, the second set of transconductors comprising at least two balanced transconductors, the at least two balanced tranconductors being self-connected, the at least two self-connected balanced tranconductors being connected between two terminals of balanced input and output ports of the electronic filter; wherein the at least two self-connected balanced tranconductors compensate the balanced resistive loss across the electronic filter and the at least two cross-connected balanced tranconductors and the at least two self-connected balanced tranconductors compensate the unbalanced resistive loss across the electronic filter.
 2. The system of claim 1 wherein the first set of transconductors and the second set of transconductors are tunable.
 3. The system of claim 1 wherein positive inputs of the at least two self-connected balanced transconductors are connected to positive outputs of the at least two self-connected balanced transconductors and negative inputs of the at least two self-connected balanced transconductors are connected to negative outputs of the at least two self-connected balanced transconductors.
 4. The system of claim 1 wherein the loss compensation by the first set of balanced transconductors and the second set of self-connected balanced transconductors in the electronic filter is balanced.
 5. The system of claim 1 wherein the at least two cross-connected balanced transconductors and the at least two self-connected balanced transconductors comprise at least one cross-coupled pair of transistors.
 6. The system of claim 1 wherein the electronic filter comprises at least one LC filter.
 7. The system of claim 6 wherein the LC filter further comprises one or more inductors and one or more varactor diodes connected to each other.
 8. An IF filter in a double conversion TV tuner utilizing the system of claim
 1. 